SSM2529ACBZ-R7 datasheet(18/52 Pages) AD

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SSM2529

Data Sheet

Rev. 0 | Page 18 of 52

Figure 36. Treble Band Frequency Response Across Gain Settings

DYNAMIC RANGE CONTROL

The dynamic range control function is used to alter (usually

reduce) the dynamic range of the audio signal so that a loud

signal can be heard without disturbing the hearing perception,

and a weak signal can still be heard. In addition, very large signals

and very weak signals are usually treated with different methods

to ensure the overall sound quality. The DRC functions include the

following:

•

Limiter

•

Compressor

•

Expander

•

Noise Gate

The dynamic range is not altered when the signal level is in the

middle. These functions can be enabled or disabled individually.

Limiter

If the input audio samples are large, the output is clipped at a

predefined level so that the speakers are not overdriven.

If the ADC power tracking function is enabled, the maximum

output level is set automatically to correspond to the speaker

SPKVDD power.

Compressor

The compressor is used to reduce the signal dynamic range

when the input level is large and within predefined boundaries.

This helps reduce the loudness when the signal level is high.

Expander

The expander is used to increase the signal dynamic range when

the input signal level is small and within predefined upper and

lower boundaries. This helps increase the loudness when the

signal is weak.

Noise Gate

When the signal level is lower than a predefined threshold level,

it is treated as noise. Under this condition, the output is set to zero.

The overall DRC characteristics are illustrated in Figure 37. A

number of threshold levels (referred to the input) are used, which

are defined as the limiter threshold (LT), compressor threshold

(CT), expander threshold (ET), noise gate threshold (NT),

maximum output signal amplitude (SMAX), and minimum output

signal amplitude (SMIN). The corresponding bits are DRC_LT,

DRC_CT, DRC_ET, DRC_NT, DRC_SMAX, and DRC_SMIN

and can be found in Register 0x59 to Register 0x5D.

Figure 37. DRC Input/Output Relationship

DRC MODE CONTROL

The DRC_EN bits in Register 0x60 control the DRC. The noise

gating function can be disabled by setting the NG_EN bit in

Table 17. DRC Mode Control Register

VBAT_

LIM_

SRC

LIM_

COMP_

EXP_EN

NG_EN

DRC_EN

Table 18. Bit Description of DRC Mode Control Register

Bit Name

Description

Settings

VBAT_EN

VBAT tracking enabled

0: disable

1: enable

LIM_SRC

Limiter source selection

0: peak

1: RMS

LIM_EN

Limiter enabled

0: disable

1: enable

COMP_EN

Compressor disabled

0: disable

1: enable

EXP_EN

Expander enabled

0: disable

1: enable

NG_EN

Noise gating enabled

0: disable

1: enable

DRC_EN

DRC enabled

0: disable

1: enable

–15

–10

–5

100M

10M

100k

10k

FREQUENCY (Hz)

INPUT

SMAX

POINT1

(LT, SMAX)

POINT2 (CT, CT)

POINT3 (ET, ET)

POINT4 (NT, SMIN)

SMIN

LIMITER

COMPRESSOR

LINEAR

EXPANDER

NOISE GATE

WITHOUT DRC

WITH DRC

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